As either an alternative or a supplement to vacuum or electrostatic chucks, substrates are often secured to a support platform within a deposition chamber by a clamp ring during sputtering or vapor deposition of material onto the substrate. Generally metallic, clamp rings are typically annular disks received on an upper surface of the substrate within the deposition chamber (e.g., by motion of a retractable support platform raising the substrate into contact with the clamp ring), exerting (together with the support platform) compressive force on the peripheral edge of the substrate to hold the substrate fixed during processing and reduce warping.
Because the clamp ring contacts the substrate surface onto which material is deposited and itself generally has material deposited thereon during deposition, “bridging” of deposited material between the clamp ring and substrate may cause the substrate to stick to the clamp ring. To avoid or minimize such bridging, the clamp ring may only contact the upper surface of the substrate at regularly spaced peripheral locations.
In addition, the clamp ring may include an edge exclusion lip around an inner circumference between and around these contacts or tabs, projecting over the peripheral edge of the substrate to inhibit deposited material from passing through the gap between the clamp ring and the substrate and around the substrate edge (i.e. by forming a tortuous path for passage through that gap). Particularly when the support platform is only nominally larger than the substrate, deposition vapors or materials passing around the edge of the substrate (and support platform) may adhere to surfaces below the support platform and may, for example, form aggregate deposits over time which impede proper operation of a retractable platform.
The design of contact surfaces and edge exclusion lips for clamp rings thus involves trade-offs between minimizing the potential for bridging, limiting passage of deposition material around the substrate and support platform edges, and shadowing no more of the substrate surface than necessary with the edge exclusion lip (as the shadowed regions become unusable). In that regard, the lip width (the distance by which the lip projects over the edge of the substrate, shadowing the underlying portions of the substrate and rendering them unusable) is balanced against lip height (the distance between the lip's bottom surface and the substrate, where closer proximity of the lip to the substrate renders bridging more likely).
U.S. Pat. No. 5,810,931 discloses a clamp ring with an edge exclusion lip having a stepped bottom surface or “roof,” where the variable profile of the lip's lower surface allows a greater effective aspect ratio of total lip width to minimum lip height despite a decrease in one or both dimensions. A presently available commercial embodiment of that clamp ring is suitable for deposition of thin aluminum layers. However, when used during deposition of thick (<2 μm) aluminum-copper (AlCu) and other metal alloy layers, including aluminum-silicon-copper (AlSiCU) and copper (Cu), and particularly during hot deposition of such layers, both the life (i.e, the number of lots which may be run before problems such as sticking arise) and the throughput (e.g., the number of lots which may be run before a cool-down period is required) for the clamp ring are substantially reduced.
There is, therefore, a need in the art for an improved clamp ring providing edge exclusion with acceptable life and throughput for aluminum-copper alloy deposition, particularly hot deposition of thick aluminum-copper alloy layers.